Negative feedback power supply apparatus

ABSTRACT

In a power supply apparatus for a load such a toroidal core testing apparatus, an input current is supplied to the load, and an output voltage of the load is obtained. A current corresponding to one part of the output voltage is negatively fed back to the input current.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a negative feedback power supplyapparatus for a load. For example, the present invention is applied toan apparatus for testing the AC magnetization characteristics of atoroidal core or a cut-core type core, a power supply apparatus for aload of a rectifier circuit, or a power supply apparatus for a load fora distorted current.

(2) Description of the Related Art

In order to carry out a testing of the AC magnetization characteristicsof a large number of toroidal cores, such as exciting currents, and acore loss such as a vortex current loss and a hysteresis loss, it isnecessary to wind windings on a core for every test. To simplify thiswinding operation, connector-type contacts may be used to reduce thedesorption of the windings. However, in the actual design oftransformers or the like, since the thickness of the windings is aslarge as possible, to reduce the resistance value thereof, and thenumber of turns of the windings is large, a current flowing therethroughis small and the reduction in potential and heat generation by theresistance component of the windings is also small. Contrary to this,when the connector-type contacts are used, since the space forinstalling the connector-shaped contacts is restricted, the thickness ofthe windings is small and the number of turns of the windings is small.As a result, it is necessary to increase a test exciting currentsupplied to the primary winding, but such a current is affected by theresistances of the windings and the contacts.

In a prior art testing apparatus for a toroidal core having primary andsecondary windings, an input AC power supply and an AC current meter areconnected to the primary winding, and an AC voltage meter is connectedto the secondary winding. Further, a power meter is connected betweenthe primary winding and the secondary winding. In this apparatus, ameasurement of a primary current I_(P) and a measurement of a core lossare carried out at the periphery of a saturated magnetic flux, which isone of the AC magnetization characteristics to be tested. Note that themeasurement of core loss is made by the power meter.

However, fluctuation of the equivalent DC resistance of the primarywinding is caused by the heat generated by the exciting current, andfluctuation of the contact DC resistance of a connector-type contact iscaused by the state of the contact. Further, fluctuation of theequivalent AC resistance of the primary winding is caused by thesaturation characteristics of the core. Therefore, a large fluctuationoccurs in the output voltage of the secondary winding. Further, at theperiphery of a saturated magnetic flux density, an extraordinary currentgenerated locally at one cycle of the AC current invites a spontaneousreduction in the equivalent AC resistance, and as a result, the waveformof the output voltage generated at the secondary winding is greatlydistorted. This large fluctuation and distortion lead to the generationof a large fluctuation and distortion in the magnetic flux density ofthe core, which is very disadvantageous from the viewpoint of obtaininga definite AC magnetic flux density. Accordingly, to make the outputvoltage of the secondary winding constant, even when the voltage of theAC power supply is adjusted so as to correct the output voltagegenerated in the secondary winding W₂, the distortion of the magneticflux density waveform, i.e., the distortion of the output voltage,remains and, simultaneously, the peak current portion of the excitingcurrent is suppressed. Therefore, it is impossible to carry out acorrect measurement.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a powersupply apparatus for testing a core, whereby a winding operation usingconnector-type contacts is unnecessary, an adjustment of an inputvoltage for every core is unnecessary even when the DC resistance andthe equivalent AC and DC resistances of the primary winding are changedby the contacts, and no distortion is generated in the magnetic fluxdensity of the core, thereby enabling a correct and stable measurement.

Another object of the present invention is to provide a power supplyapparatus for a load such as a load of a rectifier circuit and adistortion current load.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below with reference to the accompanyingdrawings, wherein:

FIG. 1 is a diagram showing suggested examples of tests of windings;

FIG. 2 is a circuit diagram illustrating a suggested apparatus fortesting a toroidal core;

FIGS. 3A and 3B are equivalent circuit diagrams of the apparatus of FIG.2;

FIG. 4 is a diagram showing the output characteristics of the apparatusof FIG. 2;

FIG. 5 is a circuit diagram illustrating a first embodiment of the powersupply apparatus according to the present invention;

FIG. 6 is an equivalent circuit diagram of the apparatus of FIG. 5;

FIG. 7 is a diagram showing an oscillation phenomenon generated in theapparatus of FIG. 5;

FIGS. 8 and 9 are timing diagrams schematically explaining a basicprinciple of the present invention;

FIGS. 10 and 11 are circuit diagrams illustrating second and thirdembodiments, respectively, of the power supply apparatus according tothe present invention; and

FIG. 12 is a diagram showing the output characteristics of theapparatuses of FIGS. 10 and 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a suggested power supply apparatus for a toroidal core, i.e., asuggested apparatus for testing a toroidal core, will be explained.

As illustrated in FIG. 1, to test a toroidal core 1, test windings W₁and W₂ may be wound on the core 1. In this case, in order to simplifythe winding operation, connector-type contacts CW₁ and CW₂ are providedto reduce the desorption of the windings W₁ and W₂. In an actual designof transformers and the like, since the thickness of the windings is aslarge as possible, to reduce the resistance value thereof, and thenumber of turns of windings is as large as possible, a current flowingtherethrough is small and the reduction in potential and heat generationby the resistance component of the windings is also small. In FIG. 1,however, since the space for installing the connector-type contacts CW₁and CW₂ is restricted, the thickness of the windings is small and thenumber of turns of the windings is small. As a result, it is necessaryto increase an exciting current or testing supplied to the primarywinding W₁, and in addition, such a current is affected by theresistances of the windings W₁ and W₂ and the contacts CW₁ and CW₂. InFIG. 1, note that upper and lower contacts of the connector-typeconnectors CW₁ and CW₂ are separated from each other when the core 1 isinserted thereinto, and are connected when a testing (measuring)operation is carried out, and thus a winding operation of the windingsW₁ and W₂ is unnecessary.

In FIG. 2, a testing apparatus for the toroidal core 1 having the testwindings W₁ and W₂ is illustrated. In FIG. 2, reference numeral 2designates an input AC power supply, 3 an AC current meter, 4 an ACvoltage meter, P₁ and P₂ terminals for the connection of the primarywinding W₁, and S₁ and S₂ terminals for the connection of the secondarywinding W₂. According to this circuit, a measurement of a primarycurrent I_(P) and a measurement of core loss are carried out at theperiphery of a saturated magnetic flux of the core 1, which is one ofthe tests of AC magnetization characteristics. Note that the measurementof core loss is made by a power meter W.

In order to easily understand the circuit of FIG. 2, an equivalentcircuit thereof is illustrated in FIG. 3A, and a simplified equivalentcircuit is illustrated in FIG. 3B. Note that the power meter W isomitted from FIGS. 3A and 3B. In FIG. 3A, reference T designates anideal transformer, R_(P) an equivalent DC resistance of the primarywinding W₁, R_(C) an equivalent contact DC resistance of the connectorcontact CW₁, and R_(ZP) an equivalent AC resistance of the primarywinding W₁. Note that the resistances of the secondary winding W₂ andthe contact CW₂ are negligible. For example, the equivalent DCresistance R_(P) and the equivalent DC resistance R_(C) are unstable.That is, the resistance R_(P) fluctuates from 1 to 1.2 Ω due to thegeneration of heat by the exciting current I_(P), and the contact DCresistance R_(C) fluctuates from 0 to 0.8 Ω due to the state of thecontact CW₁. Also, the equivalent AC resistance R.sub. ZP fluctuatesfrom ∞ to 0.5 Ω due to the saturation characteristics of the core 1.Therefore, if the voltage of the AC power supply 2 is 1 V, and anexciting current I_(P) is supplied to the primary winding W₁, the outputvoltage E_(S) of the secondary winding W₂ is 1 V where R_(P) =1 Ω, R_(C)=0 Ω and R_(ZP) =∞Ω, and 0.2 V where R_(P) =1.2 Ω, R_(C) =0.8 Ω, andR_(ZP) =0.5 Ω, which means that the fluctuation of the output voltageE_(S) is large. Further, at the periphery of a saturated magnetic fluxdensity of the core 1, an extraordinary current generated locally at onecycle of the AC current invites a spontaneous reduction in theequivalent AC resistance R_(ZP), and as a result, the waveform of theoutput voltage E_(S) generated at the secondary winding W₂ is greatlydistorted. This large fluctuation and distortion leads to the generationof a large fluctuation and distortion in the magnetic flux of the core1, which is very disadvantageous in view of the need to obtain adefinite AC magnetic flux. Accordingly, to make the output voltage E_(S)constant, when the voltage of the AC power supply 1 is adjusted so as tocorrect the voltage E_(S) generated in the secondary winding W₂, thedistortion of the magnetic flux waveform, i.e., the distortion of theoutput voltage E_(S), remains as illustrated in FIG. 4, andsimultaneously, the peak current portion of the exciting current I_(P)is suppressed. Therefore, it is impossible to carry out a correctmeasurement.

In FIG. 5, which illustrates a first embodiment of the present inventionapplied to a testing apparatus for a toroidal core, an analog negativefeedback loop circuit is added to the elements of FIG. 2. That is, anamplifier 5, a feedback resistor 6, and a phase adjusting circuit 7formed by a capacitor 71 and a resistor 72 are added to the elements ofFIG. 2. Note that FIG. 6 is an equivalent circuit diagram of theapparatus of FIG. 5.

Here, assume that there is no negative feedback circuit, theamplification factor F of the amplifier 5 having an output impedance Ois 100, and the voltage of the AC power supply 2 is 1 V×1/100=0.01 V.Then, the circuit of FIG. 5 is substantially the same as that of FIG. 2,and therefore, if the values of the equivalent DC resistance R_(P), theequivalent contact resistance R_(C), and the equivalent AC resistanceR_(ZP) are the same as in FIG. 3A, the output voltage E_(S) is alsochanged from 1 to 0.2 V. That is, if a total amplification factor A' isdetermined by the ratio of the input voltage (=0.01 V) of the AC powersupply 2 to the output voltage E_(S), the factor A' is fluctuated by

    A'=100˜20.

Next, consider the presence of the negative feedback circuit accordingto the present invention. Here, the feedback ratio F is made 0.99 by thefeedback resistor 6, the output voltage E_(S) can be represented by##EQU1## where E₁ is the output voltage of the AC power supply 2 and is,in this case, 1 V. Therefore, the maximum o voltage E_(S) ##EQU2## andthe minimum of the output voltage E_(S) ##EQU3## Thus, the fluctuationof the output voltage E_(S) is reduced compared with the case of FIG. 3A(FIG. 3B). Therefore, even when the DC resistance by the contacts, andthe equivalent AC and DC resistances of the primary winding W₁ arefluctuated, a substantial adjustment of the input voltage isunnecessary, and as a result, the distortion of the magnetic fluxwaveform in the core 1, i.e., the distortion of the output voltageE_(S), is reduced. Note that, if the amplification factor of theamplifier 5 is increased to increase the feedback factor F, thestability of the output voltage E_(S) can be improved. However, when thefeedback factor F is increased, an oscillation phenomenon may occur dueto the leak reactances of the windings. Such an oscillation phenomenoncan be suppressed by adjusting the resistor 71 and/or the capacitor 72of the phase adjusting circuit 7, to a certain extent.

In the circuit of FIG. 5 having an analog negative feedback circuit, anaccurate measurement can be obtained for a directional silicon steelcore having a magnetic flux density of about 17,000 gauss. Also, when anextremely distorted exciting current I_(P) is supplied to the primarywinding W₁ thereby generating a saturated magnetic flux density of about18,000 to 20,000 gauss in the core 1, both the feedback factor F and theamplification factor A' must be increased to obtain a highly accurateand stable measurement. In this case, however, an oscillation phenomenonalways occurs. That is, when the amplification factor A' is larger than1 and a phase shift amount in the negative feedback loop circuit islarger than 180°, the oscillation conditions may be satisfied. Such aphase shift amount is commonly generated by the capacitance component inthe negative feedback loop circuit in a relatively high frequencyregion, and in addition, it is difficult to completely adjust such aphase shift amount by the phase adjusting circuit 7. It is alsodifficult to adjust this phase shift amount when an inductance componentdue to the windings and the leak inductances therebetween is added tothe negative feedback loop circuit.

Thus, in the core 1 having a relatively high magnetic flux density, evenif an analog negative feedback loop circuit is used, the output voltageE_(S) of the secondary winding W₂ is still distorted and unstable. Thatis, in the circuit of FIG. 5, after the oscillation conditions aresatisfied in the analog negative feedback loop circuit, a positivefeedback control at a specific frequency of about 10 KHz to 1 MHz istriggered by differential noise or the like, and as a result, theamplitude of the input voltage applied to the core 1 is rapidlyincreased as illustrated in FIG. 7.

In FIGS. 8 and 9, which show a digital negative feedback controlaccording to the present invention, to prevent the generation of apositive feedback phenomenon in the negative feedback loop circuit, awaveform to be negatively fed back is stored and is delayed by one cycleof a basic sine-wave, and thereafter, a negative feedback control iscarried out by using the delayed waveform. That is, as illustrated inFIG. 8, a voltage error between an input sine-wave voltage and an outputvoltage is stored and delayed for a period A, and the input sine-wavevoltage is corrected by the delayed voltage error for a period B.Therefore, as illustrated in FIG. 9, even when a phase shift amount inthe negative feedback loop circuit is larger than 180°, a positivefeedback phenomenon is split for every cycle of the basic sine-waveform, so that oscillation is not generated.

In FIG. 10, which illustrates a second embodiment of the presentinvention realizing the principle of FIGS. 8 and 9, which is alsoapplied to an apparatus for testing a toroidal core. In FIG. 10, adigital negative feedback loop circuit is provided. That is, referencenumeral 1001 designates a control portion (CPU); 1002 a frequencyswitch; 1003 a voltage set switch formed by digital switches; 1004 abasic sine-wave generating circuit (ROM) for generating a sine-wavevoltage E₀ ; and 1005 a voltage adjusting circuit (multiplier) foradjusting the output of the basic sine-wave generating circuit 1004. Inthis case, the frequency of the basic sine-wave voltage E₀ of the basicsine-wave generating circuit 1004 is changed by the control portion 1001in accordance with the state of the frequency switch 1002. That is, thecontrol portion 1001 generates a clock signal having a frequency inaccordance with the state of the frequency switch 1002 and transmitsthis clock to the basic sine-wave generating circuit 1004. Also, thecontrol portion 1001 generates a voltage factor a in accordance with theoutput of the voltage set switch 1003. As a result, the voltageadjusting circuit 1005 multiplies each digital value of the basicsine-wave voltage E₀ by the voltage factor α to generate a new basicsine-wave voltage E₀ '.

Reference numerals 1006 and 1007 designate delay memories for adjustinga total delay time corresponding to one cycle of the basic sine-wavevoltage E₀ (E₀ '). Each of the delay memories 1006 and 1007 may beconstructed by a bidirectional memory in which a write operation and aread operation can be simultaneously carried out. That is, the delaymemories 1006 and 1007 are associated with address counters 1006a and1007a, respectively, and therefore, the delay memories 1006 and 1007 areoperated by write addresses WA and read addresses RA of the addresscounters 1006 and 1007, which are counted up by clock signals of thecontrol portion 1001. In this case, the delay time period of the delaymemory 1006 (1007) is determined by

    (RA-WA)×T

where

RA is a read address;

WA is a write address; and

T is a frequency period of the clock signal supplied from the controlportion 1001.

A subtraction circuit 1008 calculates a digital voltage error ΔE betweenthe basic sine-wave voltage E₀ ' and an analog/digital (A/D) convertedoutput voltage E_(S) from the ends of the secondary winding W₂ via anA/D converter 1012. Also, an adder circuit 1009 adds the delayed voltageerror ΔE to the basic sine-wave voltage E₀ '. A D/A converter 1010performs a D/A conversion upon the output of the adder circuit 1010, andas a result, a power amplifier 1011 supplies an input current I_(P) tothe primary winding W₁ in accordance with the analog voltage of the D/Aconverter 1010.

Thus, the output voltage E_(S) of the secondary winding W₂ is negativelyfed back by the digital negative feedback loop circuit formed by theelements 1006, 1008, 1007, and 1012. In addition, a waveform to be fedback is delayed for one cycle of the basic sine-wave voltage E₀. As aresult, the output voltage E_(S) is stable, as illustrated in FIG. 12,even when the magnetic flux density of the core 1 is extremely large.

In FIG. 11, which illustrates a third embodiment of the presentinvention, a delay memory 1101, an address counter 1101a, and an addercircuit 1102 are added to the elements of FIG. 10. In this case, thethree delay memories 1006, 1007, and 1101 adjust a total delay timeperiod corresponding to one cycle of the basic sine-wave voltage E₀ (E₀'). Therefore, in FIG. 11, the voltage error ΔE' to be fed back issummed and added to the basic sine-wave voltage E₀ ', thereby remarkablyincreasing the feedback factor F. For example, if the feedback factor Ffor the first cycle is 0.9, the feedback factor F for the second cycleis 0.99. Also, the feedback factor F for the third cycle, the fourthcycle, . . . is 0.999, 0.9999, . . .

Note that the second and third embodiments of FIGS. 10 and 11 can becombined with the first embodiment of FIG. 5. That is, an analognegative feedback loop circuit formed by the elements 6 and 7 of FIG. 5is added to the circuit of FIGS. 10 or 11, as indicated by dotted lines.In this case, the power amplifier 1011 also serves as the differentialamplifier 5 of FIG. 5. As a result, it is possible to completely correctthe output voltage E_(S) at an even higher speed.

Also, in the above-mentioned embodiments, the primary winding W₁ and thesecondary winding W₂ can be of a type other than the connector-type.Also, it is possible to carry out a highly accurate and stable testing(measurement) even when the number of turns of the windings is 1. Also,the arrangement and installation of the contacts CW₁ and CW₂ can befreely determined. Further, the number of turns of the primary windingW₁ need not be the same as that of the secondary winding W₂.

Further, the present invention can be applied to an apparatus fortesting a separate-type core, and the present invention can be stillapplied to other power supply apparatuses such as a power supplyapparatus for a load of a rectifier circuit, or a power supply apparatusfor a distorted current load.

As explained above, according to the present invention, for example, ina core testing apparatus, a winding operation for each core isunnecessary, and a correct and stable test (measurement) can be carriedout without adjusting the input voltage, even when the magnetic fluxdensity of a core is extremely large.

We claim:
 1. A power supply apparatus for a load, comprising:means for abasic sine-wave voltage; means, connected to said basic sine-wavevoltage generating means and an output of said load, for detecting avoltage error therebetween; means, connected to said voltage errordetecting means, for delaying said voltage error by one cycle of saidbasic sine-wave voltage; means, connected to said basic sine-wavevoltage generating means and said delaying means, for adding said delayvoltage error to said basic sine-wave voltage; and means, connectedbetween said adding means and said load, for supplying an input currentto said load in accordance with the result of addition by said addingmeans.
 2. An apparatus as set forth in claim 1, further comprising anegative feedback loop connected between the output of said load andsaid input current supplying means.
 3. An apparatus as set forth inclaim 1, wherein said load comprises a core having a primary winding anda secondary winding wound thereon,said input current supplying meanssupplying said input current to said primary winding, said outputvoltage being a voltage between ends of said secondary winding.
 4. Apower supply apparatus for a load, comprising:means for generating abasic sine wave voltage; means, connected to said basic sine wavevoltage generating means and output of said load, for detecting avoltage error therebetween; means, connected to said voltage detectingmeans, for delaying said voltage error by one cycle of said basic sinewave voltage; means, connected to said voltage error detecting means andsaid delaying means, for adding said delayed voltage error to saidvoltage; and means connected between said adding means and said load,for supplying an input current to said load in accordance with theresult of addition by said adding means.